Ultrasonic color imaging characterizing ultra-fine structures and continuously distributed physical conditions

ABSTRACT

This invention discloses methods and apparatus for ultrasonic color imaging that characterizes ultra-fine structures and distributional physical conditions within the target under inspection. The disclosed complementarily incorporates information arising from a plurality of repeated sound trips forced by repeated reflections of exterior and interior interfaces of target, and expresses the information into an image segment representing the main path that ultrasonic signals traveled within the target. The image produced is substantially more discriminative, descriptive, and position-sensitive to both acoustic interfaces and distributional acoustic characteristics of the target. The invention is especially useful for thin sheet targets most vulnerable to both non-continuous and continuous interior defects. The continuous interior conditions and effects of ultra-thin layered structures, that traditional ultrasonic inspection has been unable to express, are effectively expressed by linking their effects of deforming the waveform of passing ultrasonic signals to color image details.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional application“Ultrasonic Sectional Profiling Using Multi-Reflection Information inMulti-Parameter Color Image Presentation”, Ser. No. 60/707,940, filed onAug. 15, 2005 by the present inventor.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT

Not Applicable.

INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISK

None.

VOCABULARY AND DEFINITIONS

Trace, signal trace, amplitude trace, amplitude response: All thesephrases are used to refer to same thing—varying signal amplitude as afunction of time. It is also known as “A-Scan” (meaning Amplitude-Scan)in ultrasonic NDT community. Usually can be directly and reliablyobtained, a signal trace provides the most first-hand informationresource for almost all ultrasonic inspections, including thicknessgauging, flaw detection, and imaging.

Main path associated with a trace: In typical situations of ultrasonicinspection, after a detecting ultrasound signal is launched into atarget being inspected, multiple ultrasound echoes are generated bymultiple reflections between the front wall and back wall of the target.The common path of all these echoes is a straight line perpendicular tothe front wall. It often coincides with the transducer axis if the frontwall surface of target is flat and in good contact with the transducersurface. That common echo path is the main path associated with thetrace. Some portions of ultrasound signals do depart from the main pathin propagation because of scattering, diffraction, incident angle ofreflections, etc., that why a phrase “main path” seems necessary. A mainpath is actually associated with a transducer position at which thetrace is retrieved.

Imaging parameters: an equivalence of “procedure parameter”,“intermediate parameter”, or “operation parameter” widely found inliteratures on hardware and software of digital equipments. Since the“procedure” and “operation” in this document focus on image or imaging,“imaging parameter” is used wherever “procedure parameter”,“intermediate parameter”, or “operation parameter” can be used. Animaging parameter can be a physics parameter, a mathematics parameter, asignal parameter and other parameter.

Color parameter: typical color images use three quantities to uniquelyspecify the display color of each and every image point. For example, inmost widely used RGB (Red-Green-Blue) color scheme, three dimensionlessnumerical values are used to specify the amount of Red, Green and Bluerespectively. These dimensionless numerical values are referred to ascolor parameters. Besides RGB and RYB (Red, Yellow, Blue), RYGB (Red,Yellow, Green, Blue), some six-base-color color schemes also have beenreported and actually employed in color imaging equipments or mediumplatforms.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to the field of non-destructive ultrasonicmedical and industrial inspections. In particular it relates toultrasonic color imaging for medical and material inspection andcharacterization.

(2) Description of Related Art

Taking advantage of the fact that ultrasound can travel through articlebodies unreachable by human vision, ultrasonic inspection has beenwidely employed in industrial material inspection and medical diagnosisfor a long time. When a traveling ultrasound signal encounters anacoustical interface dividing two materials of different acousticimpedances, a portion of ultrasound energy enters into the forwardmaterial, while the remaining part of signal energy is bounced back tothe backward material, generates a detectable ultrasound echo revealingthe existence of the interface. Acoustical interfaces capable ofgenerating ultrasound echoes include the exterior surfaces enclosing thetarget body, as well as the interior discontinuities such as layeredstructures, voids, cracks, impurities and any abrupt changes in acousticimpedance.

The most popular ultrasonic inspection products can be classified intothree major categories: Ultrasonic thickness gauges, Ultrasonic flawdetectors, and Ultrasonic imaging systems.

Ultrasonic thickness gauges measure the time span between two echoesreflected by two interfaces of interest, typically the front and backwalls of the target. The thickness, i.e. the distance between the twowalls, is readily calculated through the measured time span and thesound speed of the target material. Numerical thickness readings arethen displayed on a screen or stored in a data file.

Ultrasonic flaw detectors display a selected portion of received signaltrace carrying information about the target interior. Interiordiscontinuities on the traveling path of incident ultrasound reflect thepassing signal, causing extra echoes to appear in the received signaltrace. Advanced flaw detectors provide auxiliary tools such asprogrammable gates, thresholds, cursors, etc, to help locating echoes ofpredetermined amplitudes within predetermined ranges.

Ultrasonic imaging systems rely on moving an ultrasound beam across thetarget surface to produce an image of the target interior. The scan ofsound beam can be realized either by mechanically moving the probe, orby electronically moving the sound beam formed by a phased transducerarray. The produced images are either cross-sectional profilesperpendicular to the scan surface, or a reflecting interface underneathand roughly parallel to the scan surface. The brightness of each imagepoint is determined by the intensity of the echo signal attributable tothe corresponding field point within the target.

In all three categories of ultrasonic inspections described above, it isthe geometries of the exterior and interior discontinuities that areactually being studied. As a matter of fact, for every field point on aninterface, there could be multiple echoes providing information, andeach echo supplying a series of numerical data representing signalamplitude as a function of time; In sharp contrast, for all image pointsbetween the interfaces (not on the interfaces), there are no datarepresenting/describing them. That is why traditional ultrasonicinspection only inspects interfaces (or discontinuities) within thetarget.

Many critical physical conditions without distinct geometric boundaries,such as variations in elasticity, density, hardness, stiffness,strength, compositional distribution, metallographic properties, etc.may develop due to diseases, medical treatments, machine processing,material fatigue, uneven strain stresses, temperature gradations,physical strikes, prolonged exposure to physical or chemical effects,etc., are potentially harmful but not in the scope of ultrasonicinspections. It would be highly desirable to detect such conditionsbefore they develop into fatal discontinuities like cracks.Unfortunately, traditional ultrasonic inspections only deal withdiscontinuities, not continuously distributed conditions.

In traditional ultrasonic imaging, only one parameter, typically thepeak amplitude of the first echo, is used as the across board imagingparameter. Field points producing echoes of same peak amplitude arerepresented with same brightness, therefore seem identical to imageviewers. It can not be farther from the truth. In fact, echoes withequal peak amplitudes can be quite different in their waveforms. Thewaveform difference can reveal critical difference not only about twofield points, but also about the paths that the sound traveled to reacheach field points. Unfortunately, such invaluable information has beenleft unused in conventional ultrasonic imaging for decades.

A major improvement was disclosed by the present inventor in patentapplication “Methods and Apparatus for Ultrasonic Color Imaging”,Application Number 2004100745612 filed with China patent office on Sep.8, 2004, PCT Application Number PCT/CN2004/001030 on Sep. 8, 2004, andapplication Ser. No. 11/369,603 filed with USPTO on Mar. 7, 2006, allclaiming the benefits of same named provisional patent application filedon Sep. 8, 2003 with China Patent Office.

With the improvement disclosed in these filings, every image point isspecified by three color parameters derived from entire echo waveform,not just from the peak of the echo. Field points producing echoes ofsame peak amplitudes but different waveforms are effectivelydistinguished by different color compositions. Continuous medium body ispresented in a color composition determined by the interfaces confiningthe medium. However, this improvement is still limited in the way thatimage points on the same sound path (same scan line) and confined by thesame pair of interfaces are represented either identically, or inmonotonically changing manner. In reality, the acoustic properties nearthe interfaces typically vary in a non-linear and non-monotonous manner,the closer to the interface, the more dramatic the acoustic variationis. Prior to the present invention, no effective means of characteringor imaging such acoustic conditions are commercially available.

Some very thin sheet targets, such as the blades of an aircraft engineor power generator operating at extremely high speed, while being mostvulnerable to interior defects, are the hardest to inspect byconventional ultrasonic inspections, due to the simple fact that tinyechoes generated by defects are buried in much larger echoes contributedby the front and back exterior walls. Continuous defects that distortrather than reflect sound signals, are by far more harmiftl to thintargets than to thicker targets, but are even harder to detect.

The usefulness of any inspection is largely determined by its visualimpacts to the operator. First, visual sense communicates with brainmost efficiently. The information that a single glimpse sends to thebrain, if to play out in audio frequencies, can take years of listening.In technical language, visual sense possesses a bandwidth significantlybroader than other human senses do. Secondly, visual sense has uniquespatial perception. Not only the existences of all the objects withinthe sight, but also the spatial attributes such as dimensions, shapes,relative positioning with each other, can be learned via visual sensealmost instantly without training.

In terms of spatial perception and efficiency, visual presentations ofall ultrasonic inspections are not equal. The best presentation is thestereoscopic real time images, such as a pumping heart, a breathinglung, or a live baby moving in mother's womb. Not surprisingly, thismost desired presentation, known as four dimensional imaging, isproduced by very expensive ultrasonic imaging systems.

On the other end, the numerical thickness readings presented byultrasonic thickness gauges, although efficient in conveying measurementresults, provide no spatial perception. A numerical reading is notvisually related to the spatial attributes like size or spacing.“0.9999” and “1.0000” look very different but are practically equal,while “0.07” and “0.01” seem more alike but differ drastically. Manythickness gauges use a sound beep to alert the occurrence of pre-definedthickness reading, indicating that numerical readings alone can notfulfill the task satisfactorily. Moreover, in erosion inspection ofextended pipelines or gigantic high pressure vessels, hundreds eventhousands thickness measurements are needed to locate the worst erosionspots. In such common and demanding inspection tasks, an appropriateimage is definitely better than piles of numerical readings.

Signal traces, always used but not necessarily explicitly displayed byall ultrasonic inspection equipments, carry valuable information notshown in numeric readings and traditional images. A false thicknessreading, due to severe noises or overlap of multiple echoes, often canbe identified from the signal trace. However, users are unable, or tolarger extent, unwilling to deal with signal traces because of theirpoor visual image. It is a demanding task, even for well trained NDTprofessionals, to identify flaws through tiny echoes buried in muchlarger interfering echoes and background noises. Whenever possible, mostinspectors rather take the straightforward numeric readings overinsightful signal traces.

Ultrasonic erosion inspection and flaw detection are rarely performed byimaging systems despite of all the merits of image, not only becauseimaging systems are prohibitively expensive for typical NDT operationbudgets, but also due to the operability limitations of imaging systems.Transducer arrays used in medical imaging can manage an adequateacoustical contact with soft human bodies, but not on rigid, curvedsurfaces and small facets, and are not practical when the test spotshave narrow accesses, high temperature, or other severe conditions.Mechanical scan require good acoustic coupling between the transducerand target without changing target's positioning, which is achievedeither by running a stream of coupling agent between the transducer andthe target throughout the inspection, or by immersing the scan mechanismin a tank filled with coupling agent (water or oil)—not feasible formost NDT situations.

Above discussions indicate three much needed improvements in ultrasonicinspection: a) inspection or characterization for continuouslydistributed physical/acoustical conditions; b) inspection orcharacterization for very thin sheets; c) an inexpensive, practical wayto generate visual images in ultrasonic erosion inspection, flawdetection and other common and demanding NDT tasks.

SUMMARY OF THE INVENTION

The objective of the present invention is to provide a combined solutionto all three above discussed challenges that the prior art has failed toanswer in decades.

The present invention discloses apparatus and methods of a new categoryof ultrasonic inspection with the following merits:

-   -   a) Presentation wise, it possesses the efficiency and spatial        perception of images, the straightforwardness and exactness of        numerical readings, and the informational richness and        insightfulness of signal traces.    -   b) Hardware cost wise, it is in line with ultrasonic flaw        detectors, and is significantly less expensive than ultrasonic        imaging systems.    -   c) Applicability wise, it works on any spots where traditional        NDT flaw detection or erosion inspection can be performed.    -   d) Functionality wise, it covers the traditional tasks of        thickness gauging, flaw detection and significant part        ultrasonic imaging, with drastically improved performance in        characterization of thin sheets with or without interior        discontinuities—the most challenging task in ultrasonic        inspection.    -   e) Operation wise, the intuitively understandable visual        presentation, and the significantly reduced rate of false        detection and failed detection, making ultrasonic NDT        significantly easier and preferable.

BRIEF DESCRIPTION OF THE OF THE DRAWING

FIG. 1 illustrates the signal trace generated by a 5 MHz transducer on a5 mm thick calibration block.

FIG. 2 illustrates the signal trace generated by the same 5 MHztransducer on a 1 mm thick calibration block.

FIG. 3 illustrates an impulse response derived from the signal trace inFIG. 2. Impulse response is actually the signal trace when theexcitation signal is a perfect impulse.

FIG. 4: illustrates the color composition of an image segment taken froma cross-sectional profile image. Due to the fact that the patent ruleson drawing don't allow color images that can't be reliably reproduced bycopy machines, the RGB color compositions are provided instead ofactually coloring the image.

FIG. 5 illustrates how the present invention compares with the prior artimaging in flowchart presentations.

FIG. 6 illustrates the data retrieval, processing, storage and displayof a preferred embodiment.

DETAILED DESCRIPTION OF THE INVENTION

This invention discloses methods and apparatus for ultrasonic colorimaging that characterizes ultra-fine structures and distributionalphysical conditions within the target under inspection. The disclosedmethod complementarily incorporates information arising from a pluralityof repeated sound trips forced by repeated reflections of exterior andinterior interfaces of target, and visualizes the information into animage segment representing the main path that ultrasonic signals havetraveled within the target. An image that is substantially morediscriminative, descriptive, and position-sensitive to both acousticinterfaces and distributional acoustic characteristics of the target, isachieved as the result.

The invention is especially useful for thin sheet targets mostvulnerable to both non-continuous and continuous interior defects. Thecontinuous interior conditions and effects of ultra-thin layeredstructures are effectively expressed in color image details.

The ultrasonic color imaging method of present invention deals withtrace of ultrasound signals that repeatedly travel on same main path dueto multiple reflections of exterior and interior interfaces of thetarget. The processes include: a) preparing an array of sequencednumerical data substantially rooted from said trace of ultrasoundsignals; b) selecting a plurality of data members from the array ofsequenced numerical data such that selected members were respectivelyand effectively influenced by same geometric position on the main pathduring different repeated trips; c) calculating a plurality of colorparameters from the selected data members, to express said geometricposition on said main path into an image element of a color image; d)for each and every geometric positions on the main path, performing b)and c) to express the overall trace into an image segment representingentire main path within the target.

The process of deriving the array of sequenced numerical data can bechosen from the following: digitization of the trace without substantialmodification; Fourier transforms of the trace; inverse convolutions orde-convolutions using the trace as a source function; digital signalprocessing for suppressing background noises, for emphasizingcontributions of pre-selected physical effects imposed by said target,and for separating contributions among repeated sound trips;combinations of above processes.

The image segments of many traces covering different main paths acrosssame target are arranged to form a cross-sectional profile of thetarget.

The image segment representing an entire path within the target iscomposed of parallel color lines. The spacing between the two edge linesis proportional to the target thickness as measured at the locationwhere the trace was recorded. The relative position of each color linewith respect to the two edge lines stands for the geometric point on themain path with same relative position with respect to two targetsurfaces. The color composition of each color line represents how thecorresponding geometric point affects the passing-by ultrasound signalsin consecutive repeated trips.

The color composition of the edge line representing front wall of thetarget may be defined by:RGB(F₀₁(y_(T) ₀ ,y_(T) ₁ ,y_(T) ₂ , . . . ),F₀₂(y_(T) ₀ ,y_(T) ₁ ,y_(T) ₂ , . . . ),F₀₃(y_(T) ₀ ,y_(T) ₁ ,y_(T) ₂ , . . . ))and the color composition of other lines may take a general form of:RGB(F₁(y_(T) ₁ _(−i),y_(T) ₂ _(−i),y_(T) ₃ _(−i), . . . ),F₂(y_(T) ₁ _(−i),y_(T) ₂ _(−i),y_(T) ₃ _(−i), . . . ),F₃(y_(T) ₁ _(−i),y_(T) ₂ _(−i),y_(T) ₃ _(−i), . . . ))where RGB(Red, Green, Blue) stands for a system-supported functiondefining display color by three color parameters for the amounts of Red,Green and Blue respectively. F₀₁ and F₁( ), F₀₂ and F₂( ), F₀₃ and F₃( )are multi-variable functions in different forms, for calculating Red,Green and Blue parameters respectively. i stands for the time needed forsound to travel a round trip between the position that the line standsfor and the back wall of the target. T₀ is the time moment of the firstfront wall echo, and T₁ through T_(n) are time moments of first throughnth back wall echoes respectively. y_(T) _(n) , y_(T) ₁ _(−i), y_(T) ₂_(−i) . . . are dada members in the array of sequenced numerical datacorresponding to T_(n), T₁−i, T₂−i respectively.

The ultrasonic apparatus disclosed by present invention comprises of: asetup of launching a detecting ultrasonic signal into a target underinspection; a setup of retrieving the trace of ultrasonic signalsresulting from the interactions between the detecting ultrasonic signaland the target; a setup of digitizing the retrieved trace and preparingan array of sequenced numerical data substantially representative of thedigitized trace; and a setup of color imaging, which further comprisesof: a) selecting a plurality of data members from the array of sequencednumerical data, the selected data members were respectively andeffectively influenced by a given geometric position on the main pathduring different repeated sound trips; b) calculating a plurality ofcolor parameters from the selected data members to express that givengeometric position into an element of a color image; c) repeating a) andb) for all geometric positions on the main path so that the overalltrace is expressed into an image segment representing the entire mainpath within the target.

Launching detecting signals into the target, retrieving the resultingsignal traces, digitizing signal trace into digital form, processing thedigitized trace into sequenced data arrays with different mathematicmethods, etc., all are typical elements in the prior art that build theplatform for the present invention. The core of present invention isusing a sequenced data array to generate a color image segmentcontaining the information related to multiple repeated sound trips onthe same sound path, while the prior art generates a gray-scale imagesegment containing only the information of a single sound trip on thesame path. Any skilled C++ programmer knowing how to work with dataarrays and how to draw color lines connecting a pair of geometric pointscan implement the present invention on the platform of a prior artultrasonic inspection device.

It is a major objective of the present invention to provide new tools ofproducing desirable image presentation for common NDT operations withoutthe high costs and operability limitations of traditional ultrasonicimaging. This goal is achieved by the disclosed ultrasonic apparatuswhich allows taking image segments at operator's will withoutrestrictions. The image segments are not arranged according to therelative geometric positions of corresponding main paths. Instead, theobtained image segments are displayed in sequential order of tracetaking operation, unless the operator wants otherwise. The resultedcross-sectional profile does not comply with rules of traditionalimaging, but well serves the purpose of comparing obtained imagesegments to identify abnormal interior condition—exactly what thepresent invention wants.

The disclosed ultrasonic apparatus also supports: storing apredetermined number of signal traces; a movable cursor allowing theoperator to highlight any image segment in the displayed profile tobring up the additional information associated with the highlightedsegment, including: entire or a selected portion of corresponding signaltrace, an array of sequenced numerical data rooted from the trace,thickness reading and other numeric quantities characterizing the signaltrace, numeric quantities characterizing all stored traces as a group,the information display is independent of the main display—thecross-sectional profile composed of many segments for the operator tochoose. In such a way, the apparatus performs the functionality ofthickness gauging, flaw detection, and other inspection tasks. Thecross-sectional profile serves a visual organizing and accessing toolfor all information available from all stored signal traces.

Preferred Embodiments (1) An Embodiment Based on Signal Trace

FIG. 1 shows the signal trace generated by a 5 MHz transducer on a 5millimeter thick calibration block (the target). The echo in third andfourth divisions is the first back wall echo. The second back wall echooccupies divisions 5 and 6. The third back wall echo spans divisions 7through 9. The waveform in first and second divisions is the triplesuperposition of electrical excitation impulse, acoustic excitationsignal, and the front wall echo. It is impossible to tell the threeapart from each other. Without a clean front wall echo, target thicknessd can be determined by the spacing between the first and second backwall echoes. In the following we present three different images, allbased on the same trace shown in FIG. 1.

-   -   a) The image segment generated by traditional ultrasonic        imaging, so called B-image (Brightness image), is composed of        two bright line segments parallel with each other in black        background, representing two exterior walls of the target. With        the front wall echo not available, the line segment representing        front wall is given a fixed brightness value, say 255. The line        segment representing back wall is displayed with a brightness        proportional to the peak amplitude of first back wall echo. In        the trace of FIG. 1, that is 0.62*255=158. The spacing between        the two line segments represents the target thickness at the        location where the trace was recorded. If the display resolution        is 5 pixels per millimeter, then the spacing is 25 pixels,        indicating a thickness of 5 millimeter.    -   b) The image segment generated by the color imaging method prior        to the present invention, disclosed in U.S. patent application        Ser. No. 11/369,603 by present inventor, is composed of two        color line segments in white background. The positioning and        spacing of two line segments are the same as the brightness        image. Again, without front wall echo waveform, the front wall        is assigned a reference color, say RGB(255, 255, 255). The        meaning of RGB( ) function is covered in the discussion of color        parameter in VOCABULARY AND DEFINITIONS. The back wall color is        defined by RGB(x₁, x₂, x₃), where x₁, x₂ and x₃ are three color        parameters derived from the waveform of the first back wall        echo. For simplicity, we relate them to the amplitudes of three        largest lobes of echo waveform. Obviously, color image based on        three parameters responds to waveform distortion therefore        discriminates more material conditions than one parameter based        brightness image which responds only to amplitude reduction. The        space between the two edge lines can be filled with color        RGB(255−x₁, 255−x₂, 255−x₃).    -   c) The image segment generated by a trace-based embodiment of        present invention looks quite similar to the above case.        Nevertheless, with information of three back wall echoes to be        incorporated into the image, the image of back wall can be much        more insightful. According to the reflection theory, the        waveform distortion before and after reflection relates to the        reflection characteristics of the interface. Only a perfect        reflection makes no change to waveform. The waveform distortion        can be implemented into the image as follows:        -   Suppose A₁, B₁, C₁ stands for amplitudes of three largest            lobes of first back wall echo. Similarly, A₂, B₂, C₂ are            corresponding parameters for second back wall echo, and A₃,            B₃, C₃ for the third back wall echo. Here the subscriptions            indicate which echo the parameter belongs to. The color            composition of back wall is implemented as RGB(X, Y, Z),            where            X=255*(A ₂ /A ₁);            Y=255*a*(2*(A ₂ /A ₁)−(B ₂ /B ₁)−(C ₂ /C ₁));            Z=255*b*(2*(A ₃ /A ₂)−(B ₃ /B ₂)−(C ₃ /C ₂));        -   For a perfect reflection, the ratio of corresponding            parameters between two echoes should be all identical, i.e.            A₂/A₁=B₂/B₁=C₂/C₁, and A₃/A₂=B₃/B₂=C₃/C₂, therefore Y=Z=0.            Since X is the amount of Red composition, the image color of            back wall is pure red. The intensity of red color is            proportional to A₂/A₁, the reflection ratio or reduction of            signal size. That is, in the case of perfect reflection,            this embodiment of present invention and the traditional B            ultrasonic imaging are essentially identical. However, when            faced with real life, imperfect reflections by imperfect            interfaces, the multiple-echo-based color imaging of present            invention can quantitatively describe the imperfections via            color parameters Y and Z, while the traditional imaging            pretends the imperfections don't exist. Constant factors a            and b can be adjusted to emphasize or de-emphasize the            effects of second and third echoes respectively. This            embodiment is only one of numerous possibilities enabled by            imaging an interface with three echoes instead of a single            parameter from a single echo.

The greatest merit of basing imaging on signal trace is easy toimplement. The negative side, however, is well demonstrated by thesignal trace in FIG. 2, where echoes from front and back walls are alloverlapped together, no analysis and measurement is possible withoutmajor advances in analyzing methods or tools. That is the determiningfactor of introducing the next embodiment.

(2) An Embodiment Based on Acoustic Impulse Response of Target

It was a major goal of present invention to provide a characterizationtool for continuous acoustic medium body, especially the medium in thinsheet or near interior interfaces and exterior boundaries. Such newcapability should be achieved to complement, not to compromise theexisting capability of detecting interfaces or discontinuities. Thisgoal is successfully realized by a preferred embodiment based onacoustic impulse response of target.

FIG. 2 shows the signal trace generated by a 5 MHz transducer on a 1millimeter thick calibration block. The waveform dramatically differsfrom the one in FIG. 1, not only because of the overlap among echoes,but also because of the waveform change of each individual echo. For atarget in 1 mm thickness range, the distribution of acoustic propertiesis dominated by surface effects as a function of distance from targetsurface. The non-monotonous nature in acoustic properties dramaticallyreshapes the waveform of passing-by sound signals even without anydiscontinuities. The present invention effectively incorporates thewaveform reshaping characteristics of a target into a cross-sectionalimage, revealing variation of acoustic properties as a function of depthfrom the target surface.

A signal trace is dominated by two primary factors: a) the transducercharacteristics independent of target; b) the accumulated acousticaleffects of the sound path within the target. In the case of a thin sheettarget, the main path is traveled multiple times. Since the purpose ofultrasonic NDT is inspecting the target, not the transducer, it ishighly desirable to separate the target (the sound path) effects fromthe transducer effects. An effective way of achieving such separation isderiving the impulse response of the sound path from the trace.

Impulse response plays a center role the linear filter theory—afoundation of digital signal processing. When an input signal goesthrough a system (such as a target under inspection), the signalwaveform experiences a specific reshaping process determined by thecharacteristics of the system. The resulting output signal can beexpressed, to the extent of linear approximation, as the mathematicconvolution of the input waveform and the impulse response of thesystem. Technically, if the waveforms of input signal and output signalare both known, the impulse response of the system can be calculated viainverse convolution (de-convolution) or Fourier analyses. Accordingly,if the signal waveform before entering the target and the signal traceare known, the impulse response of the target can be computed. Therehave been plenty of publications on computing impulse response of asystem from the input and output signals. Finding a generic way ofcomputing impulse response from signal trace for widely diverseapplications has not been fruitful. It was not an objective of presentinvention to provide methods of obtaining impulse response from signaltrace. Rather, the present invention focuses on utilizing a signaltrace, an impulse response, or other sequenced data collections rootedfrom a signal trace to produce cross-section color profiles bestcharacterizing the target.

FIG. 3 shows an impulse response derived from the trace in FIG. 2. Whencomputed properly, the impulse response of a complete sound path tellsthe exact timing of each reflection (therefore the exact location ofeach interface), as well as how the waveform is altered by eachreflection. By theory, only a perfect reflection generates an echoperfectly replicating the incident signal. The impulse response of aperfect reflection is a single vertical line of unity height standing ontime axis at a location representing the timing of the reflection. Sincethere is no such thing as perfect reflection in real life, reflectionsencountered in NDT inspections typically have an impulse response of atall vertical line surrounded by several leading and trailing shortlines, as can be seen in FIG. 3. The cleanliness of the impulse responsedirectly represents the pureness of the reflection. The interiorscattering, attenuation, diffractions, side wall reflections, roughnessand incident angle relative to the interface, etc., all contribute tothe waveform reshaping (including but not limited to size reduction) andshowing their effects in the signal trace. The impulse response derivedfrom a trace characterizes acoustic effects much better than the traceitself does, because the interfering effects of transducer in the tracehave been eliminated, at least significantly reduced.

The preferred embodiment utilizes impulse responses calculated from thesignal trace to minimize the transducer effects before thickness andflaw analysis. Unavoidably, the quality and performance of thetransducer still play a role through affecting the accuracy of obtainedimpulse response. However, the transducer characteristics impact thetrace much more significantly and unpredictably than they impact thecomputation of impulse response. The impulse response approach is mostadvantageous for thin targets generating multiple, overlapped echoes, anightmare of traditional ultrasonic NDT for decades.

FIG. 4 shows a cross-sectional profile image produced by a preferredembodiment. The profile is composed of a number of side-by-side colorsegments. Each segment is further composed of a stack of equal sizedcolor straps. One of the color segments is enlarged to demonstrate howthe present invention differs from the gray-scale, prior-art ultrasoundimaging that fills the segment with a brightness either un-varying, ormonotonically varying between the opposite boundaries.

The height and width of all color straps remain unchanged for entireimage, and are solely determined by the vertical and horizontal imageresolutions (object-size per pixel) respectively. The target thicknessat the spot where the signal trace was retrieved is proportional to thetotal height of all straps in the stack, and determines the number ofstraps in the segment. Every color strap is filled with a colorcomposition defined by a set of color parameters exclusively assigned tothis strap. In such a way, the variations in composition andphysical-property, either along the target surface or across the targetdepth, are effectively presented via color variations. Any unusualmaterial conditions, whether continuous or discontinuous, can causedramatic changes in the color pattern of the corresponding segment,draws attentions from the operator.

The thickness is the most critical information in forming an imagesegment, must be determined as the first step. Let's use FIG. 3 to showthe process of a preferred embodiment. The first vertical line in blackstands for the reflection by the front wall. The highest blue verticalline stands for the first reflection by the back wall. Let T be thehorizontal distance between the black line and highest blue line, itthen represents the time needed for sound to travel a round trip betweenthe front and back walls. With T known, thickness d at the test spot canbe readily calculated by d=0.5 T*v, where v is the sound speed of thetarget material, factor 0.5 counts for the fact that T is the time for around trip.

Traditionally, T is determined from the trace. Drawing T from an impulseresponse is easier and much more reliable. In fact, a trace works onlywhen the target is thick enough so that the echoes generated by frontwall and back wall are clearly separated from each other, as the case inFIG. 1. The thinner the target gets, the smaller the separation betweenadjacent echoes becomes, until the echoes overlap on each other. Whenthis happens, more sophisticated methods, such as impulse response,frequency analysis, etc. have to be employed to correctly determine thetime intervals between the overlapped echoes. As declared earlier, thepresent invention does not provide the method of computing impulseresponse from a trace, rather, it covers a method of producing colorcross-sectional profile from a known impulse response.

Once T, the time period needed for sound to travel a round trip betweenthe two exterior surfaces, is correctly determined, the location of allechoes corresponding to multiple reflections can be easily calculated.Let T₀ be the time moment at which the front wall reflection takesplace, T₁, T₂, . . . T_(n) be the time moments of the 1^(st), 2^(nd) andthe nth reflection by the back wall, the following relation applies:T _(i) =T ₀ +i*T i=1,2, . . . n  Eq. (1)This relation holds both for signal trace and impulse response.

The multiple reflections in a trace provide a rich information resourceabout the acoustic conditions of the target. The information isinherited by mathematical transforms rooted from signal trace, such asthe impulse response, Fourier transform, etc. The process described hereapplies to other mathematical transforms.

Impulse response is actually a special case signal trace,—the traceobtained with an ideal transducer generating a spike-shaped signalwaveform with no leading or trailing ringing. The better the transducersignal can be approximated by an impulse, meaning the front wall echohas narrow and high main lobe with few and small ringing, the moreaccurately the impulse response can be derived from the signal trace.

In the impulse response in FIG. 3, T₀, the timing of the front wall echois the horizontal location of the black line, and T₁, the timing of thefirst back wall echo is the horizontal location of the highest blueline. T, the time period for sound to travel a round trip between thefront and back walls of the target, is calculated by T=T₁−T₀. With T andT₀ known, T₂ through T_(n) are calculated by Eq. (1). In softwareimplementation, T₀ through T_(n) are integer indexes of an integer arrayallocated for storing the impulse response.

The segment height stands for target thickness at the spot where thetrace was obtained. It is proportional to T. Suppose T equals N sampleintervals, the segment is then composed of N+1 horizontal color lines ofequal width. The top and bottom lines represent the front and backwalls, with color composition determined by data value at locations T₀through T_(n), i.e. the heights of vertical lines at locations T₀through T_(n) in FIG. 3. Let us denotes them by y_(T) ₀ through y_(T)_(n) .

The color composition of top edge of profiles in FIG. 4 was implementedasRGB(y_(T) ₀ ,y_(T) ₀ −y_(T) ₁ ,y_(T) ₀ −y_(T) ₂ )  Eq. (2)While the composition of bottom edge was defined asRGB(y_(T) ₁ ,y_(T) ₂ ,y_(T) ₃ )  Eq. (3)It is important to understand that y_(T) ₁ , y_(T) ₂ , y_(T) ₃ ,although representing reflections taking place with clearly separatedtiming, are attributable to same target point—the back wall spot thatintersects with the sound path. By Eq. (2) and (3), the top edge colorcomposition is dominated by the front wall echo y_(T) ₀ while the bottomedge color gives equal weights to first three back wall reflectionsy_(T) ₁ , y_(T) ₂ , and y_(T) ₃ . Expressions in Eq. (2) and (3) can befreely redefined to shift the emphases from one reflection to another toaddress different application purposes.

Expression (2) seems a little fancy than it needs to be. There is areason for it. In ultrasonic inspection practice, a signal trace notonly depends on target and transducer, but also strongly depends onacoustical coupling between the transducer and the target. In otherwords, the outcome of inspection can strongly depends on how theinspector holds the transducer on the target surface. By Eq. (2), theimage of the top line strongly dependents on y_(T) ₀ , the front wallsignal, therefore is sensitive to the coupling, providing an convenientway for checking the coupling consistence.

A line in the middle of top and bottom lines with a distance i from thebottom, is implemented to have a color compositionRGB(y_(T) ₁ _(−i),y_(T) ₂ _(−i),y_(T) ₃ _(−i)), i=1,2, . . . N−1.  Eq.(4)By running i from 1 through N−1, all the color lines in the segment areindividually defined by three data members in the impulse response.Again, y_(T) ₁ _(−i), y_(T) ₂ _(−i), y_(T) ₃ _(−i), although withdifferent timing in different round trips, are equally distanced fromT₁, T₂, T₃ respectively, therefore describe the same geometric point inthe target body. Data members from different trips can be incorporatedin describing a single image point as long as these data members areattributable to the same corresponding field point. Consider a cracklocated at i sample intervals from the back wall, causing extrareflections at time moments T₁−i, T₂−i, T₃−i, i.e., causing y_(T) ₁_(−i), y_(T) ₂ _(−i), y_(T) ₃ _(−i) to be much larger than theirneighbors, resulting the ith color line counting from bottom to besignificantly darker than other lines. If y_(T) ₁ _(−i), y_(T) ₂ _(−i),y_(T) ₃ _(−i) were applied to other field points, more than one linewould be wrongfully strengthened, suggesting more than one cracks.

As an ultrasound signal travels within the target body, the waveformreshapes itself and signal amplitude decreases along the way. Echoes ofhigher reflection order, say second or third echoes, travel longerdistance, interact with more target interior therefore carry richerinformation about the target interior. The negative side is that echoesof higher orders are contaminated by more noises and other unwantedinterferences. The preferred embodiment gives operator an option ofweighing the reflections of different orders differently for differentapplication needs. Expression (4) can be generalized asRGB(F₁(y_(T) ₁ _(−i),y_(T) ₂ _(−i),y_(T) ₃ _(−i), . . . ),F₂(y_(T) ₁ _(−i),y_(T) ₂ _(−i),y_(T) ₃ _(−i), . . . ),F₃(y_(T) ₁ _(−i),y_(T) ₂ _(−i),y_(T) ₃ _(−i), . . . )) i=1,2, . . .N−1.  Eq. (5)where F₁( ), F₂, F₃( ) stand for three different multi-variablefunctions for calculating the Red, Green and Blue parameters in RGBcolor system. By changing the definition of F₁( ), F₂, F₃( ), sectionalprofiles emphasizing different interior characteristics can be achieved.

Let's use the acoustic impulse response in FIG. 3 to exemplify how acolor segment is processed.

Suppose the acoustic impulse response in FIG. 3 is stored in data arrayy[ ] containing 400 data members. The 39^(th) and 72^(nd) data membershave data values much more significant than others, representing theamplitudes of the reflection by the front wall and the first reflectionby the back wall respectively. T₀, the timing of the front wallreflection therefore is 39, while T₁, the timing of the first back wallreflection is 72. T, the time period for sound to travel a round tripbetween the front and back walls, is 72−39=33 (equals the total timetaken for collecting 33 data samples). Using Eq. 1, T₂ and T₃ can bereadily calculated as 105, 138 respectively. The amplitudes of thecorresponding reflections are found in data members y[39], y[72],y[105], and y[138]. The color composition of the top edge of the segmentcan be calculated by plugging y[39], y[72], y[105] in Eq.2. Similarly,the color composition of the line right below the top edge is obtainedby inserting y[40], y[73], y[106] in Eq. 4. Then, y[41], y[74], y[107]are put in Eq. 4 for the next line . . . until the bottom line in thesegment is reached, which has a color composition defined by RGB(y[72],y[105], y[138]). The information of multiple reflections (after beingtransformed into the impulse response) is thus incorporated into a colorsegment of a sectional profile.

The interior scattering, attenuation, diffractions, side wallreflections, roughness and incident angle relative to the interface,etc, all contributed to the size reductions and waveform reshaping ofthe signal trace recorded. The present invention provides an effectiveway of incorporate all these acoustical effects into a singlecross-sectional segment. If interior conditions underneath certaininspection spots have changed because of material fatigue, straindamages, temperature gradations, physical strikes, prolonged exposure tophysical or chemical effects, etc, the color image of the correspondingsegment will differ from that of other segments, revealing the location,as well as many details of the condition changes.

By linking the segment image to a front wall echo and several back wallechoes, a single color image brings out by far more interiorcharacteristics than traditional, one-echo-based ultrasonic imaging. Theresulting cross section profile is by far more discriminative andsensitive to tiny variations, as well as to their geometricdistributions inside the target. Whether the variations are abrupt orgradual, near to or far away from the exterior walls, constructively ordestructively overlapped, as long as there are any waveform reshapingeffects, the preferred embodiment can show them in the cross-sectionalprofile image.

The traditional imaging complies with rules of positioning,proportioning and completeness, i.e., each image element (a pixel or agroup of pixels) must be placed at the right position with respect toother image elements, with consistent proportion, and the entire targetbody within the scope is imaged without omission. When a transducerarray or a computer automated mechanic scanning system is use, scanparameters such as scan routes and scan steps, are used both for scancontrol and for image construction, automatically assures positioning,proportioning and completeness. A controlled scan mechanism has alwaysbeen an integral part of the traditional ultrasonic imaging.

The preferred embodiment imposes no restriction on selection ofinspection spots. In the default display mode of Cross SectionalProfile, a new segment is place to the right of existing profile forevery new trace obtained at a new spot. Any spots can be visited at anytime regardless of positioning, proportioning and completeness. Theinspection spots can be scattered in any direction with any spacing; canbe tested/re-tested in any order; can be clearly separated from oroverlapped with each other; can be on the same smooth surface or ondifferent facets of a target, even on different sub-targets. A profileimage composed of segments taken at such un-regulated spots, althoughuntraditional, but serves NDT purpose even better.

In NDT applications, more often than not, the real purpose is detectingabnormal or potentially harmful spots rather than pursuing a completeinterior image of the target. How the underneath of a target spotmaterially compares with other portions of target is often moreimportant than the actual visual appearance of the spot. The preferredembodiments provide a visual presentation concentrating on detectingabnormal from normal, rather than on pursuing rigorousness andcompleteness of the imaging process. The reward of losing traditionalsense of image is achieving the flexibility not allowed by traditionalimaging systems, as well as the visual advantages not possessed by flawdetectors.

Erosion inspection of large scale equipments is a major applicationtargeted by the present invention. Consider a large chemical vessel withits wall thickness varying between 0.95 through 1.05. Although afluctuation less than 10%, the updates of thickness readings in thedisplay window of a thickness gauge keep operator's eyes and mind busyand wearing out. When a really alarming reading 0.35 does appear, itsvisual impact is no more that the impact of 0.95. Only if the beep alarmis active and alarm threshold has been set properly, a sound alert canbe issued to save the visual incompetence. Alternatively, the preferredembodiment displays a series of side-by-side profile segments separatedby a narrow vertical blank. The height of a segment is proportional tothe wall thickness of the corresponding test spot, visually andstraightforwardly shows how the wall thickness varies with the testspots. Without any knowledge about thickness range and thresholdsetting, without unnecessary nerve striking and vision fatigue, theembodiment not only catches the occurrence of a serious event, but alsotells how serious the event is with all the advantages of humanvision—effectiveness, efficiency and spatial perception. Beep alarm isstill in use, but not triggered by a pre-defined threshold setting, butby image contrast between the new segment and other existing ones.

There are some other aspects in the processing of cross-sectionalprofile. They are addressed or implemented by the preferred embodimentas follows:

The width of segment is determined by the total display width and thenumber of segments being displayed. In principle, the image out of everyamplitude response should be a single pixel wide, i.e. a vertical linein the profile. In practical applications, single pixel wide image pieceis not visually perceived well, therefore is artificially expandedhorizontal-wise. The minimum and maximum segment width should bepredefined and applied. For example, the minimum segment width can beset as 1/50 of display width, and the maximum segment width is set as1/10 of display width respectively. Say the total display width is 200pixels, the minimum and maximum segment widths are 4 pixels and 20pixels respectively. The maximum number of displayed segments is then50. The first segment in the window uses the maximum segment width, 20pixel-wide in this case. As the inspection continues and the number ofsegments increases, the widths of all displayed segments decreasegradually until the minimum segment width is reached. After the totalnumber of displayed segment reaches 50, any newly added segment willpush the segment on the left end out of the window, the segment width iskept at 4 pixels wide and the total number of displayed segments remains50. A horizontal sliding bar can be implemented to move the displayedportion of cross-sectional profile to bring the segments that have beenpushed out of the window back to the scene.

The vertical scale of display is determined by the maximum depth orthickness of the application. As an example, say the vertical displaysize is 100 pixels high, the maximum thickness is set at 1 inch, thevertical scale or the thickness resolution is then 100 pixels per inch.A target of 0.01 inch thick will be displayed as one pixel high. Severalways were implemented to address vertical resolution related issues: a)The operator can horizontally move a cursor to highlight any displayedsegment (make it current), the exact thickness reading of the selectedsegment will be displayed as numeric reading at a window locationallocated for thickness readings of current segment. b) Reset thevertical scale for better vertical resolution, say 400 pixels per inch.In cases vertical overflow of some thick segments, a vertical slidingbar can be used to move the display vertically to show the overflowedpart. c) An display mode that dynamically resets the vertical scaleaccording to the largest thickness of all segments being displayed. Thevertical resolution X pixels/inch (or mm) is automatically updated at adedicated window location.

The placement of new segment: By default, the latest segment is added tothe right end of the cross-sectional profile. The very first segment inan empty window can be placed either at the left side of the window orany location at user's choice. A segment cursor can always be movedalong the cross-sectional profile to make any segment or segment slotcurrent, brings up detailed information about the current segment, orfill the current segment slot with next available segment image. Theusage of segment cursor is implemented similarly to the cursor in PCbased word processing software that allows user to add or insert a newletter anywhere.

The alignment reference: Alignment mode is one of the image presentationsettings. Segments can be aligned either with the front or the back wallof the target. For most applications, such as erosion inspection, itmakes more sense to align with the flatter, smoother front (exterior)wall, because the thickness variation is caused by erosion on the back(interior) wall. On the other hand, if the target has flat back wall,such as a calibration block with steps of different heights, using backwall as alignment reference is the obvious choice.

Orientation of profile display: Cross-sectional profiles shown in FIG. 4are horizontally oriented. There is a Profile Orientation setting in thepreferred embodiment that allows switching between horizontal andvertical profile presentation.

1. An ultrasonic color imaging method to be applied with an ultrasoundapparatus, comprising: a) accessing a trace of ultrasound signalsprovided directly or indirectly by said ultrasound apparatus, whereinsaid trace covers repeated trips of said ultrasound signals on a samemain path within a target, and said repeated trips were forced bymultiple reflections of exterior and interior interfaces of said target,wherein said ultrasound apparatus further performs the steps of: b)preparing an array of sequenced numerical data substantially rooted fromsaid trace of ultrasound signals, c) selecting a plurality of datamembers from said array of sequenced numerical data such that selecteddata members were respectively and effectively influenced by samegeometric position on said main path during different repeated trips ofsaid ultrasound signals, and d) calculating a plurality of colorparameters from said selected data members to express said geometricposition on said main path into an image element of a color image,whereby the information arising from a plurality of said repeated soundtrips is complementarily incorporated into the color image such that thecolor image is substantially more discriminative, descriptive, andposition-sensitive to distributional acoustic characteristics of saidtarget.
 2. The ultrasonic color imaging method of claim 1, wherein stepsc) and d) are repeated for all geometric positions on said main path sothat overall said trace is expressed into an image segment representingentire said main path within said target.
 3. The ultrasonic colorimaging method of claim 2, further comprising: combining said imagesegments of said traces respectively covering different said main pathsacross said target to form a cross-sectional profile of said target. 4.The ultrasonic color imaging method of claim 2, wherein said imagesegment representing entire said path within said target is composed ofparallel color lines, the spacing between two edge lines is proportionalto the target thickness at the location where said trace was obtained,the relative position of each color line with respect to two edge linesstands for the geometric point on said main path with same relativeposition with respect to two target surfaces, the color composition ofeach color line represents how the corresponding geometric point withinsaid target affects passing-by ultrasound signals in consecutiverepeated trips.
 5. The method of claim 4, wherein the color compositionof the edge line representing front wall of said target is defined by:RGB(F₀₁(y_(T) ₀ ,y_(T) ₁ ,y_(T) ₂ , . . . ),F₀₂(y_(T) ₀ ,y_(T) ₁ ,y_(T) ₂ , . . . ),F₀₃(y_(T) ₀ ,y_(T) ₁ ,y_(T) ₂ , . . . )) and the color composition ofother lines may take a general form of:RGB(F₁(y_(T) ₁ _(−i),y_(T) ₂ _(−i),y_(T) ₃ _(−i), . . . ),F₂(y_(T) ₁ _(−i),y_(T) ₂ _(−i),y_(T) ₃ _(−i), . . . ),F₃(y_(T) ₁ _(−i),y_(T) ₂ _(−i),y_(T) ₃ _(−i), . . . )) where RGB(Red,Green, Blue) stands for a system function defining display color bythree color parameters quantifying the amounts of Red, Green and Bluerespectively; F₀₁ and F₁( ), F₀₂ and F₂( ), F₀₃ and F₃( ) aremulti-variable functions in different forms, for calculating Red, Greenand Blue parameters respectively; i stands for the time needed for soundto travel a round trip between the position the line stands for and theback wall of said target; T₀ is the time moment of the first front wallecho, and T₁ through T_(n) are time moments of first through nth backwall echoes respectively, y_(T) _(n) , y_(T) ₁ _(−i), y_(T) ₂ _(−i) . .. are dada members within said array of sequenced numerical datacorresponding to T_(n), T₁−i, T₂−i respectively.
 6. The ultrasonic colorimaging method of claim 1, wherein said preparing process of said arrayof sequenced numerical data is selected from a group comprising:digitization of said trace without substantial modification, Fouriertransforms of said trace, inverse convolutions or de-convolutions usingsaid trace as a source function, digital signal processing forsuppressing background noises, digital signal processing for emphasizingcontributions of pre-selected physical effects imposed by said target,digital signal processing for separating contributions among repeatedsound trips, and combinations thereof.
 7. An ultrasonic apparatuscomprising: a setup for launching a detecting ultrasonic signal into atarget under inspection, a setup for retrieving a trace of ultrasonicsignals resulting from interactions between said detecting ultrasonicsignal and said target, wherein said interactions include repeated soundtrips on same main path caused by repeated sound reflections by exteriorand interior interfaces of said target, a setup for digitizing saidretrieved trace and preparing an array of sequenced numerical datasubstantially rooted from the digitized trace, and a setup for colorimaging, comprising: a) a setup for selecting a plurality of datamembers from said array of sequenced numerical data such that selecteddata members were respectively and effectively influenced by a givengeometric position on said main path during different repeated trips ofsaid detecting ultrasound signal, b) a setup for calculating a pluralityof color parameters from said selected data members to express saidgiven geometric position into an element of a color image, and c) asetup for repeating a) and b) for all geometric positions on said mainpath so that overall said trace is expressed into an image segmentrepresenting entire said main path within said target, wherebyinformation arising from a plurality of repeated sound trips caused byrepeated sound reflections by the exterior and interior interfaces ofsaid target is complementarily incorporated into said color image suchthat the image is substantially more discriminative, descriptive, andposition-sensitive to distributional acoustic characteristics of saidtarget.
 8. The ultrasonic apparatus of claim 7, wherein said array ofsequenced numerical data is selected from a group comprising: (a)digitized trace without substantial modification, (b) Fourier transformsof said digitized trace, (c) inverse convolutions or de-convolutionsusing said digitized trace as a source function, (d) impulse responsesotherwise derived from said digitized trace, (e) digital data afterdigital signal processing for suppressing background noises, (f) digitaldata after digital signal processing for emphasizing contributions ofpre-selected physical effects imposed by said target, (g) digital dataafter digital signal processing for separating contributions among saidrepeated sound trips, and any combinations of (a) through (g).
 9. Theultrasonic apparatus of claim 7, further comprising: a setup forcombining image segments of multiple said traces respectivelyrepresentative of different main paths across said target in thesequential order of trace taking operation or in operator specifiedmanner, regardless of relative geometric positioning among said mainpaths, to form a cross-sectional profile of said target, whereby theformed cross-sectional profile serves the purpose of comparing obtainedimage segments to identify abnormal interior condition, rather thangenerating rigorous image in traditional imaging sense.
 10. Theultrasonic apparatus of claim 9, further comprising: a setup for storinga predetermined number of said multiple traces, devices such as amovable cursor allowing operator to select any image segment based onone of said stored traces, a setup for displaying additional informationbased on said stored trace independently of the display of saidcross-sectional profile, wherein said additional information is selectedfrom a group comprising: entire or a selected portion of said trace,entire or a selected portion of transformed or modified said trace,entire or a selected portion of an impulse response based on said trace,thickness reading and other numeric quantifies characterizing saidtrace, numeric quantities characterizing multiple stored traces as agroup, and any combinations thereof, whereby the apparatus performs thefunctionality of ultrasonic thickness gauging, ultrasonic flawdetection, and other ultrasonic inspection tasks using saidcross-sectional profile as a visual organizing and accessing tool.